Vehicles include a drivetrain that may include a charge sustaining or charge depleting (CS/CD) hybrid propulsion configuration (which may or may not be designed to accept battery charge power from an external electric energy source, i.e., a plug in hybrid) or a range extended full electric propulsion configuration to propel the vehicle. In either configuration, the drivetrain includes an internal combustion engine, and an electrically variable transmission including a first motor/generator and a second motor/generator. The range extended full electric configuration, used in an extended range electric vehicle (EREV), must be capable of propelling the vehicle on battery power alone until the battery charge is depleted. At that time it transitions to an operating strategy similar to a conventional hybrid in which the engine is operated during some driving conditions to provide drive power and maintain battery state-of-charge. The CS/CD hybrid configuration generally requires the engine to operate in order to provide full vehicle power, and is designed to be capable of operating as an electric vehicle only at lower powers. In either configuration, vehicle propulsion may come from any of the internal combustion engine, the first motor/generator, the second motor/generator, or any combination thereof. Either configuration is also capable of charging the battery by operating one or both electric motors as a generator while the engine is running. Hybrid propulsion configurations generally require a larger internal combustion engine, and utilize smaller batteries than vehicles utilizing the full electric propulsion configuration. For example, a passenger car vehicle utilizing the full electric propulsion configuration may include a battery having a power output of greater than 100 KW, whereas vehicles utilizing the hybrid propulsion configuration may only require a battery having a power output of between 30 and 40 KW. The additional available battery power may be used to reduce the power required from the engine to provide the same vehicle performance.
The different operating strategies between the differing propulsion systems lead to substantially different usage of the electric motor/generators. For example, the electric motor/generators of the full electric propulsion configuration tend to operate at higher speeds and higher powers during operation as an electric vehicle, whereas electric motor/generators of the hybrid propulsion configuration tend to operate at lower speeds and lower powers. Additionally, one or both of the motor/generators in a full electric propulsion configuration typically require a high torque capability to provide adequate launch and reverse gradeability performance. The high torque required from the motor/generator tends to reduce the power and efficiency of the motor/generator at high speeds. Accordingly, the full electric propulsion configuration and the hybrid propulsion configuration generally employ different transmission power flows, and utilize different electric motors.
The hybrid electrically variable transmission typically includes either strong rare earth permanent magnet motors, or large induction motors, in order to attain the desired efficiency. Rare earth magnets are expensive, thereby increasing the costs of the rare earth permanent magnet motors, while the induction motors are larger and require additional packaging space.